The demand for more sustainable and energy-efficient buildings extends beyond just how they're designed. It also extends to the products that are used. In the case of curtainwalls, the emphasis on energy efficiency and thermal performance are driving high-performance curtainwall design.
Energy efficiency and thermal performance are driving factors in high-performance curtainwall design
Designed by Pappageorge Haymes Partners, 465 North Park Apartments’ curved, jewel-like curtainwall is comprised of several EFCO products, and is pursuing LEED Gold certification. (Photo: Pappageorge Haymes Partners, courtesy of EFCO Corp. and Technoform)
“There is an emphasis on improving thermal performance, whether it is through thermal breaks, using double-glazed or triple-glazed systems with two low-E coatings; or opting for very high-performance infills with even lower U-value and lower solar heat gain coefficient (SHGC) such as VIGs and electrochromics,” explains Brian Tobias, architectural representative at Tubelite Inc., Walker, Mich. “Incorporating organic and recyclable materials into the design is also seen in recent sustainable design trends. As buildings pursue LEED and other green building certifications, there is a greater demand for energy-efficient systems.”
Designing a cost-effective solution is also important, such as metal-framed framed polycarbonate systems, or systems that incorporate multiple glazing types. As Jim Leslie, general manager at EXTECH/Exterior Technologies Inc., Pittsburgh, explains, “With the push toward energy-efficient products, and at a lower price point, polycarbonate systems fill in the gaps. These systems are impact resistant. Daylighting decreases demand on electrical lighting systems. Highly insulating panels also can reduce HVAC loads, contributing to green building and energy goals.”
Façade performance is a hot topic, says J.B. Howell, national sales manager at Menomonee Falls, Wis.-based Novum Structures LLC, and is discussed from the very beginning, noting that energy efficiency determines the makeup of the glass lites used in the façade design.
Designed by SOM, 707 Fifth “AAA” office tower in downtown Calgary, Alberta, features a distinctive, curved glass appearance with high energy efficiency and a comfortable interior. (Photo: Chad Koski, courtesy of Technoform)
Thermal Performance
While designers have a variety of tools to help them achieve the needed thermal performance in a dual-pane fenestration system such as wider thermal barriers in the frame, argon gas fill, warm-edge spacer, improving the second surface low-E coating or adding a second low-E on the fourth surface, Helen Sanders, Ph.D., general manager, Glass Insulation North America at Technoform, Twinsburg, Ohio, says there has been increased demand for triple-pane units and warm-edge spacers. As she explains, including a warm-edge spacer can reduce the U-factor from 0.02-0.3 BTU/of.hr.ft2 in captured fenestration and up to 0.05 BTU/of.hr.ft2 in structurally glazed curtainwall and is an easy way to meet incrementally increasing thermal performance requirements.
Spandral performance is also becoming an issue since it is considered an opaque area, Sanders notes, but its performance is significantly worse than a wall, and thermal bridging from spandrel to transparent areas of curtainwall along continuous vertical mullions causes a reduction in thermal performance, which is not captured in NFRC 100 thermal calculations for U-factor. “Other areas of thermal bridging within the spandrel are also not adequately captured by the current 2-D simulation techniques used within the NFRC 100 standard,” she explains. “The challenges with improving spandrel performance presents designers with challenges in designing with curtainwall in areas where codes have enacted envelope backstops, which limits the trade off lower performing envelopes with higher performing internal systems. In these cases, the thermal performance of the curtainwall must come closer to or equal that of the base case system with much lower window to wall ratio.”
According to Chad Ricker, market team manager at Technoform, there is a significant trend to using more engineered plastic like glass-filled polyamide profiles to reduce the U-factor of fenestration but are engineered in a way that manages the structural requirements of architectural fenestration. What this typically means is wider polyamide thermal barriers, which become more complex to reduce convective heat transfer as well as conductive heat flows. “Companies are exploring the limits of design with plastic relative to the combination of thermal performance with structural performance and are developing creative solutions,” he says. “While aluminum is still needed for structural performance, designers are being creative with moving its position and combining with plastic profiles to minimize thermal bridging.”
Where structural requirements are not such a requirement, Ricker says fabricators are swapping out regular glass-filled polyamide with an even lower conductivity polyamide material called low lambda. “At the design stage,” he adds, “designers are also focused on reducing metal to glass ratio by, for example, removing intermediate horizontals and using deeper tubes to span further helps thermal performance by reducing the metal.”
“Non-metal pressure plates made from glass-filled reinforced polyurethane or polyamide help improve thermal performance (U-factor) and resistance to condensation,” says Tobias. “Glass-filled polyamide edge adapters are unique to curtainwall designs that help remove metal, and therefore thermal bridging, from the exterior-side of the fenestration,” adds Ricker. “In areas where there is no structural requirement, low lambda polyamide is being used to further reduce U-factors. Examples include edge protectors, which hold gaskets and form air/water barriers.”
The Buddy Holly Hall of Performing Arts and Sciences in Lubbock, Texas. (Photo: Casey Dunn Photography, courtesy of YKK AP Inc.)
Reducing Embodied Carbon
Reducing embodied carbon in curtainwalls is also important, as more designers are interested in understanding the emissions caused by the manufacture of glass and aluminum to make informed supply chain and design decisions, Sanders says. “Life cycle assessments of construction projects are starting to be done alongside operational energy modeling to make good decisions between upfront carbon emissions and emissions due to the operation of the building.”
In insulating glass, Sanders explains the main embodied carbon comes from the float process itself and whether lites are heat treated. Therefore, she says, the key to reducing embodied carbon in glass starts at the design phase when it’s determined how many lites, how thick are the lites, are they heat treated, how much area of glass is required, etc. Sanders goes on to explain, “The main embodied carbon impacts in aluminum curtainwall are the aluminum smelting and the amount of recycled content in it (more recycled content = lower emissions by weight as the recycled aluminum is basically free). The emissions from the smelting process are determined by the greenness of the electric grid used, which is typically pretty good in North America because a lot of hydro power is used in aluminum production. This is not true of aluminum from China nor the Middle East. Sourcing from sources with greener grids is likely to become a trend. In fact, the U.S. and Europe have a trade agreement in which they will give preferential tariff treatment to low carbon aluminum.”
Building Codes
As with most aspects of a building’s design, building codes can have both positive and negative effects on design trends. “A positive aspect is that codes are pushing buildings to incorporate more daylighting and become more energy efficient,” Leslie says. “However, some aspects of code have not kept pace with newer technologies, and thus place artificial constraints on the use or application of some products.”
As buildings are expected to not only withstand the elements, Schohan notes that as the world faces continuous and rapid changes in weather patterns, the International Code Council (ICC) drives the steady improvement of building and energy codes to better suit regions with changing climate and extreme weather. “However, architects and builders are also taking it upon themselves to be proactive with their high-performance product recommendations and designs,” he says. “Architects are designing curtainwall elements that are more energy-efficient and better able to withstand harsh elements such as hurricane-force winds. Clients are also requiring higher-performing curtainwall systems that may even exceed their climate zone requirements, staying ahead of the ever-increasing requirements being led by the ICC.”
High-performance curtainwall contributes to Vaisala’s net-zero-ready North American headquarters in Louisville, Colo. (Photo: Matt Puckett, courtesy of Tubelite Inc.)
Supply Chain Issues
The curtainwall industry, like every other industry these past few years, is being affected by supply chain issues, material shortages and a shortage of labor. “Shortages of field installation labor has led to more factory fabrication and assembly of glazing system,” says Leslie. “Factory-fabricated systems address many building challenges, such as field labor costs and quality control.”
Adds Tobias, “Supply chain issues, material shortages and extended lead times are causing designers to question the feasibility of custom designs relative to the project schedule. Involving the manufacturers’ architectural representatives as early as possible in the project’s planning process will provide the best selection for standard, modified and custom curtainwall that meets the aesthetic needs, performance requirements, budget and schedule.”
To make sure everyone’s needs are being met when designing curtainwall systems, it’s important to consult with manufacturers early in the design process, which Leslie explains ensures that the project can incorporate the highest performing and most economical products, without compromise to the design or intended performance.
Since budget remains a key topic of discussion around curtainwall deigns, Howell emphasizes the importance of collaboration between the entire construction team in the development of technical solutions to preserve the aesthetic and performance objects. By identifying integrated systems solutions with corresponding budget goals early in the design phase, Howell says important decisions can be made earlier in a project’s life cycle.
